We're almost to the point, technologically, where you won't have to remember a single thing.
This newfangled padlock -- called Noke -- has no keys, keyhole or combination for you to remember, instead relying on your iOS or Android device to unlock it via Bluetooth. Get within 10 feet of the thing, keep your phone in your pocket and you'll be able to unlock it. You can share access with other people as well, turn off the auto-unlock-within-10-feet feature and receive alerts whenever Noke is unlocked by someone else.
"But what if I lose my phone?!" you bellow, your face red with Internet nerd rage, your hammy fists pounding against your desk until they leave C-shaped sweat rings. You can unlock the lock by pumping the doohickies in a Morse code-like fashion you set in advance, like so:
The padlock has a battery, which lasts a year and can only be removed when the padlock's unlocked. If you manage to run it dry, there's an emergency backup feature as well. It's water resistant, and there's a special bike cable available for $20.
This is a Kickstarter project that's been fully funded, with the promise of the padlocks being shipped out early next year. Early backers can get a padlock for $59; the final retail price is set to be around $89.